Neutron diffraction evidence of double interaction between NaY zeolite and ammonia and migration of Na+ ions upon ND3 adsorption

Location and orientation of adsorbed molecules in zeolites from solid-state REAPDOR NMR

“…The error in the determined dipolar coupling strength is based on variation in the estimated dipolar coupling with different tensor orientations. It should be noted that no contribution from 27 Al was observed for on-resonance 23 Na irradiation (discussed further below). Multispin interactions between 15 N are considered negligible in this case since the NH 3 molecules are isolated from each other at this low loading.…”

“…21 This loading level corresponds to B1 NH 3 molecule per unit cell. The 15 N/ 23 Na, 15 N/ 27 Al, 1 H/ 23 Na and 1 H/ 27 Al REAPDOR NMR experiments were executed with a 4 mm triple resonance MAS probe operating at 400.15, 105.85, 104.27 and 40.55 MHz for 1 H, 23 Na, 27 Al, and 15 N, respectively. The REAPDOR sequence (see Fig.…”

“…8 1 H-15 N cross-polarization (CP) was implemented in the 15 N experiments while a 1 H p/2 pulse was used to generate initial spin magnetization in the 1 H experiments. The RF field strength for the 23 Na and 27 Al adiabatic passage pulse was 71 kHz in the 15 N detected REAP-DOR measurements and 91 kHz in the 1 H detected experiments. TPPM 1 H decoupling was applied in the 15 N REAPDOR NMR experiments.…”

“…The 15 N magic angle spinning (MAS) NMR spectrum of NH 3 adsorbed in zeolite 3A yields two primary adsorption environments that were attributed to mobile and rigidly bound NH 3 . 21 The bound NH 3 site is occupied first during adsorption and displays a significant TRAPDOR effect to both 23 Na and 27 Al irradiation, indicating a close proximity of NH 3 to both Na cations and Al framework species. To further characterize this site, the distance between the adsorbed NH 3 and the Na cation and Al framework environment was measured with 15 N/ 23 Na and 15 N/ 27 Al REAPDOR NMR, respectively.…”

The nature of cationic adsorption sites in alkaline zeolites—single, dual and multiple cation sites

“…Calorimetric and volumetric adsorption techniques continue to be used [24][25][26][27][28][29][30][31] for gathering information on the energetics of gas adsorption complexes in alkaline zeolites, but discrimination between different types of cation sites is not always possible and, besides that, neither calorimetry nor determination of isosteric heats of adsorption (from gas adsorption isotherms) can give precise information on the geometry of the adsorption complex. For the latter purpose, X-ray crystallography [32][33][34] and neutron diffraction 35 were used in some favourable cases, as well as NMR spectroscopy. [36][37][38][39][40][41][42] However, widespread use of low temperature equipment rendered IR spectroscopy a main technique for experimental characterization of zeolite adsorption sites by using probe molecules.…”